DESCRIPTION (provided by investigator): Hyperphosphorylation of Tau leads to neurofibrillary tangle (NFT) formation in Alzheimer's disease (AD) and contributes to synaptic dysfunction underlying dementia. Reduction of Tau hyperphosphorylation is a therapeutic goal in AD. O-GlcNAc is an intracellular carbohydrate post- translational modification dynamically attached/removed by enzymes. Tau is modified by O-GlcNAc, and O-GlcNAc levels are reduced in human AD brain. O-GlcNAc competes with phosphorylation at specific serines/threonines, leading to the hypothesis that reduced O-GlcNAc in AD may contribute to Tau hyperphosphorylation. The 3XTg-AD mouse displays Abeta plaques and progressively increasing hyperphosphorylation of Tau that correlates with NFT burden. We've demonstrated specific decreases in O-GlcNAc modifications that correlate with Tau hyperphosphorylation in the 3XTg-AD mouse. We've demonstrated pharmacological elevation of in vivo brain O-GlcNAc levels for the first time using a novel inhibitor of the enzyme that hydrolyzes O-GlcNAc. This elevation of O- GlcNAc reduces hyperphosphorylation of Tau at the hyperphosphorylation epitope threonine 212 in the 3XTg-AD mouse. We will map human and mouse Tau O-GlcNAc sites and comprehensively determine the influence of pharmacological in vivo elevation of O-GlcNAc levels on specific Tau hyperphosphorylation events (through western blotting, mass spectrometry, and immunohistochemistry) and NFT burden in the 3XTg-AD mouse. This project will elucidate mechanistic interplay between O-GlcNAc and phosphorylation on Tau, demonstrate a novel component regulating Tau hyperphosphorylation in AD, and define enzymes that regulate O-GlcNAc levels as novel candidate therapeutic targets in AD.